This invention relates to an apparatus and a process for the production of elastane filaments by the wet spinning method, with improved titer uniformity of the elastane filaments and an increased service life of the spinning nozzles.
Elastane filaments are currently mainly produced by two methods which are fundamentally different, namely the dry spinning method and the wet spinning method. In the dry spinning method, the spinning solvent of a solution of a polyurethane, typically in dimethylacetamide, is removed from the filaments which are spun in the spinning shaft, by hot gas in the spinning shaft and by heating the spinning shaft. In the wet spinning method for the production of elastane filaments, the elastane solution to be spun is generally pre-filtered after a degassing step and is transferred into a spinning vessel. The polymer solution is subsequently filtered, and after the optional further addition of additives the spinning solution is fed to spinning nozzles by means of metering pumps. This procedure is described, for example, by F. Fourne in Chemiefasern/Textilindustrie 44/96th Volume Year, page 365, and in U.S. Pat. No. 3 526 689.
Elastane solutions are understood to be solutions of polyurethanes or polyurethane-ureas, which are usually structured in a segmented manner from hard and soft segments, in suitable solvents such as dimethylacetamide or dimethylformamide. Depending on the area of application, polyester or polyether chains are usually incorporated in the polyurethane(-ureas) as the soft segments.
In wet spinning, the spinning nozzles are immersed in a spinning bath, whereupon the spinning solution which emerges through the orifices of each spinning nozzle coagulates when it enters the spinning bath (precipitation bath). This produces filaments which are subsequently pulled off and fed to a further treatment step. During the wet spinning of elastane filaments, in addition to the complete de-aeration of the solution which is ready for spinning, good uniformity and filtration are important prerequisites for a perfect spinning process (see F. Fourne: Chemiefasern/Textilindustrie 44/96th Volume Year, June 1994, page 394, left-hand column, 2nd paragraph).
When these process steps, which are known in principle, are adhered to, a maximum nozzle service life of about 2-3 days is generally achieved. The nozzles then start to become clogged by elastane material, and this results in filament tear-off effects in the precipitation bath and in filaments becoming wound on the deflection rolls in the immersion bath or at other production locations. The nozzles then have to be replaced, which is associated with a relatively high time consumption for the operating personnel. This time consumption is generally 3 to 5 minutes per spinning nozzle. This results in increased costs during the wet spinning operation.
Amongst their other uses, threads made of elastane filaments are employed for the production of sheet goods, woven fabrics or materials which in turn are mainly suitable for corsetry, stockings and elastic sports clothing such as bathing suits or bathing trunks.
In general, wet-spun elastane filaments exhibit good titer uniformity, with a coefficient of variation of the titer which is less than 5. However, these values are often unsatisfactory, particularly for the production of textile broadware. What are termed "baggy" regions are then formed in ready-to-wear goods, and generally result in complaints by customers.